1. i ii iii ConcepTest #1: Two spheres can be held and moved around by insulated handles; the spheres start in contact with no net charge. (i) A negative charge is brought near the spheres. (i) The spheres are separated. (iii) The charge is removed. Consider the following choices: 1. No net charge 2. Positive 3. Negative 4. Not enough information After the three steps, what would be the net charge on the right-most sphere if the two spheres were a) conductors? b) insulators?

2. ConcepTest #2: At the instant pictured, an electron is a distance r from a proton (the proton is held fixed). Consider the following choices a) At the instant picture, what direction is the force on the electron? b) At the instant pictured, what direction is the electron moving? + – r Think about This: At the location of the electron, what direction is the electric field (due to the proton)? At the location of the proton, what direction is the electric field (due to the electron)?

3. ConcepTest #3: A dipole has charges + q and – q separated by some distance. The dipole sits in a uniform electric field that points to the right. What is the direction of the net force acting on the dipole? + –

4. ConcepTest #4: A dipole has charges + q and – q separated by some distance. The dipole sits in a uniform electric field that points to the right. What is the direction of the net torque acting on the dipole? (use the “center” of the dipole as your reference point) + – Think about This: What is the magnitude of the (net) torque exerted on the dipole about its center?